1. Field of the Invention
This present invention relates generally to the field of integrated circuit manufacturing technology and, more specifically, to the deposition of titanium-containing films with low levels of chlorine contamination.
2. Description of the Related Art
This section is intended to introduce the reader to aspects of the art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the manufacturing of integrated circuits, numerous microelectronic circuits are simultaneously manufactured on a semiconductor substrate. These substrates are usually referred to as wafers. A typical wafer is comprised of a number of different regions, known as die regions. When fabrication is complete, the wafer is cut along these die regions to form individual die. Each die contains at least one microelectronic circuit, which is typically replicated on each die. One example of a microelectronic circuit which can be fabricated in this way is a dynamic random access memory.
Although referred to as semiconductor devices, integrated circuits are in fact fabricated from numerous materials of varying electrical properties. These materials include insulators or dielectrics, such as silicon dioxide, and conductors, such as aluminum, tungsten, copper, and titanium in addition to semiconductors, such as silicon and germanium arsenide. By utilizing these various materials, the various transistors, gates, diodes, vias, resistors, and connective paths comprising the integrated circuit may be formed. Because of the complexity, both in materials and in design, incorporated into integrated circuits, the integrated circuit can be designed to perform a variety of functions within a limited space.
In integrating the performance of the diverse materials and functions comprising the semiconductor device, titanium-containing thin films or layers are commonly employed for various purposes. For example, it is often desirable to increase the conductivity between an enhanced, or doped, region of the wafer and a subsequently deposited conductive layer. One method of providing this increased conductivity involves depositing a thin titanium-containing film, such as titanium silicide, over the wafer so that it covers the enhanced region prior to deposition of the conductive layer.
Thin films of titanium-containing compounds have other uses as well in the fabrication of integrated circuits. These uses include the use of a thin layer of titanium nitride as a diffusion barrier to prevent chemical attack of the substrate, as well as to provide a good adhesive surface for the subsequent deposition of tungsten. In addition, titanium-containing thin films may be used to prevent interdiffusion between adjacent layers or to increase adhesion between adjacent layers. For example, thin films of titanium nitride, titanium silicide, and metallic titanium can be deposited to facilitate adhesion and to reduce interdiffusion between the layers of a semiconductor device. Other titanium-containing films that may be useful for these or other purposes include titanium boride, titanium boronitride, titanium tungsten, tantalum nitride, and the ternary alloy composed of titanium, aluminum, and nitrogen.
The deposition of titanium-containing films is just one example of a step in the manufacture of semiconductor wafers. Indeed, any number of thin films, insulators, semiconductors, and conductors may be deposited onto a wafer to fabricate an integrated circuit. Various deposition processes may be employed to deposit such thin films, but two common processes are chemical vapor deposition (CVD) and atomic layer deposition (ALD).
In CVD, the gas phase reduction of highly reactive chemicals under low pressure results in very uniform thin films. A basic CVD process used for depositing titanium or titanium-containing films involves a given composition of reactant gases and a diluent which are injected into a reactor containing one or more silicon wafers. The reactor is maintained at selected pressures and temperatures sufficient to initiate a reaction between the reactant gases. Plasma may also be introduced to enhance some deposition reactions, i.e. plasma enhanced CVD or PECVD. The reaction results in the deposition of a thin film on the wafer. If the gases include hydrogen and a titanium precursor, such as titanium tetrachloride, a titanium-containing film will be deposited. If, in addition to hydrogen and the titanium precursor, the reactor contains a sufficient quantity of nitrogen or a silane, the resulting titanium-containing film will be titanium nitride and titanium silicide respectively.
The ALD deposition process, also known as atomic layer chemical vapor deposition (ALCVD) is a refinement of the CVD process in which the deposition of a layer of material is controlled by a pre-deposited layer of a precursor. Using the ALD technique, layers as thin as one molecule may be deposited. The ALD technique provides complete step coverage and very good conformality.
Both the CVD and ALD techniques are useful for depositing titanium-containing thin films, typically using titanium tetrachloride as a precursor. Use of titanium tetrachloride, however, has the undesired consequence of producing chlorine and chloride byproducts, i.e. Cl and/or HCl, which may contaminate the titanium-containing thin film. In addition, the reaction chamber walls are typically contaminated by the chlorine-based byproducts. Because such byproducts are weakly bonded to the walls, the byproducts contaminate future reactions and products. This chlorine and chloride contamination is problematic since chlorine is known to affect the performance of the resulting semiconductor devices adversely either by impairing the functioning of the titanium-containing thin film or by poisoning or corroding adjacent metal layers by diffusion of the chlorine contaminant. In addition, the chlorine-based byproducts may corrode the reaction chamber itself, further impairing future deposition reactions and increasing maintenance time and costs associated with the chamber.
One current technique for reducing the degree of chlorine-based contamination is exposing the thin film to ammonia gas after deposition. This technique, however, does not remove all of the chlorine-based contamination from the thin film or from the reaction chamber and requires the introduction of an additional process. Another current technique for reducing chlorine-based contamination is to increase the deposition temperature to greater than 350° C. This technique also does not remove all of the chlorine-based contamination from the thin film or from the chamber. Increased deposition temperature has the additional disadvantages of adversely affecting previously deposited films and of producing thin films with poor step coverage which can increase the failure rates of the produced dies, i.e. higher deposition temperatures typically reduce the yield of acceptable semiconductor devices. Ideally, a technique for reducing the degree of chlorine-based contamination will reduce contamination during the deposition process, not subsequently, and will operate within the preferred temperature range for the deposition process.